The process parameters of microwave hydrothermal carbonization (MHTC) have significant effect on yield of hydrochar. This study discusses the effect of process parameters on hydrochar yield produced from MHTC of rice husk. Results revealed that, over the ranges tested, a lower temperature, lower reaction time, lower biomass to water ratio, and higher particle size produce more hydrochar. Maximum hydrochar yield of 62.8% was obtained at 1000 W, 220 °C, and 5 min. The higher heating value (HHV) was improved significantly from 6.80 MJ/kg of rice husk to 16.10 MJ/kg of hydrochar. Elemental analysis results showed that the carbon content increased and oxygen content decreased in hydrochar from 25.9 to 47.2% and 68.5 to 47.0%, respectively, improving the energy and combustion properties. SEM analysis exhibited modification in structure of rice husk and improvement in porosity after MHTC, which was further confirmed from BET surface analysis. The BET surface area increased from 25.0656 m2/g (rice husk) to 92.6832 m2/g (hydrochar). Thermal stability of hydrochar was improved from 340 °C for rice husk to 370 °C for hydrochar.
The process parameters of microwave-induced hydrothermal carbonization (MIHTC) play an important role on the hydrothermal chars (hydrochar) yield. The effect of reaction temperature, reaction time, particle size and biomass to water ratio was optimized for hydrochar yield by modeling using the central composite design (CCD). Further, the rice straw and hydrochar at optimum conditions have been characterized for energy, chemical, structural and thermal properties. The optimum condition for hydrochar synthesis was found to be at a 180 °C reaction temperature, a 20 min reaction time, a 1:15 weight per volume (w/v) biomass to water ratio and a 3 mm particle size, yielding 57.9% of hydrochar. The higher heating value (HHV), carbon content and fixed carbon values increased from 12.3 MJ/kg, 37.19% and 14.37% for rice straw to 17.6 MJ/kg, 48.8% and 35.4% for hydrochar. The porosity, crystallinity and thermal stability of the hydrochar were improved remarkably compared to rice straw after MIHTC. Two characteristic peaks from XRD were observed at 2θ of 15° and 26°, whereas DTG peaks were observed at 50⁻150 °C and 300⁻350 °C for both the materials. Based on the results, it can be suggested that the hydrochar could be potentially used for adsorption, carbon sequestration, energy and agriculture applications.
Polymer composites are fabricated by incorporating fillers into a polymer matrix. The intent for addition of fillers is to improve the physical, mechanical, chemical and rheological properties of the composite. This study reports on a unique polymer composite using hydrochar, synthesised by microwave-assisted hydrothermal carbonization of rice husk, as filler in polylactide matrix. The polylactide/hydrochar composites were fabricated by incorporating hydrochar in polylactide at 5%, 10%, 15% and 20 wt% by melt processing in a Haake rheomix at 170 °C. Both the neat polylactide and polylactide/hydrochar composite were characterized for mechanical, structural, thermal and rheological properties. The tensile modulus of polylactide/hydrochar composites was improved from 2.63 GPa (neat polylactide) to 3.16 GPa, 3.33 GPa, 3.54 GPa, and 4.24 GPa after blending with hydrochar at 5%, 10%, 15%, and 20%, respectively. Further, the incorporation of hydrochar had little effect on storage modulus (G') and loss modulus (G″). The findings of this study reported that addition of hydrochar improves some characteristics of polylactide composites suggesting the potential of hydrochar as filler for polymer/hydrochar composites.
Increased COVID-19 vaccine hesitancy presents a major hurdle in global efforts to contain the COVID-19 pandemic. This study was designed to estimate the prevalence of adverse events after the first dose of the Covishield (AstraZeneca) vaccine among physicians in Bangladesh. A cross-sectional study was conducted using an online questionnaire for physicians (n = 916) in Bangladesh. Physicians who received at least one dose of the COVID-19 vaccine were included. The study was carried out from April 12 to May 31, 2021. More than 58% of respondents (n = 533) reported one or more adverse events. Soreness of the injected arm (71.9%), tiredness (56.1%), fever (54.4%), soreness of muscles (48.4%), headache (41.5%) and sleeping more than usual (26.8%) were the most commonly reported adverse events. Most vaccine-related reactogenicities were reported by the younger cohorts (<45 years). The majority of respondents reported severity of reactogenicity as "mild," experienced on the day of vaccination, and lasting for 1-3 days. The most common reactogenicity was pain at the injection site; the second most common was tiredness. Almost half (49.2%) of the physicians took acetaminophen (paracetamol) to minimize the effects of vaccine reactogenicity. Multivariate logistic regression analyses showed that physicians with diabetes and hypertension (OR = 2.729 95% CI: 1.282-5.089) and asthma with other comorbidities (OR = 1.885 95% CI: 1.001-3.551) had a significantly higher risk of vaccine-related reactogenicities than physicians without comorbidities. Further safety studies with larger cohorts are required to monitor vaccine safety and provide assurance to potential vaccine recipients.